Control apparatus for an internal combustion engine

A control apparatus for an internal combustion engine comprising:

• a catalyst disposed in an exhaust passage of said internal combustion engine;
• a downstream air-fuel ratio sensor disposed downstream of said catalyst in said exhaust passage;
• a target air-fuel ratio setting section configured so as to set, based on an output value of said downstream air-fuel ratio sensor, a target upstream air-fuel ratio which is a target value of an air-fuel ratio of a gas flowing into said catalyst to a target rich air-fuel ratio and a target lean air-fuel ratio, alternately;
• a fuel injection valve configured so as to inject a fuel to said engine;
• a fuel injection control section configured so as to determine a fuel injection amount which is an amount of said fuel injected from said fuel injection valve in accordance with said target upstream air-fuel ratio, and so as to have said fuel injection valve inject said fuel of said determined fuel injection amount;
• an evaporated fuel purge section configured so as to introduce an evaporated fuel generated in a fuel tank storing said fuel supplied to said fuel injection valve into an intake passage of said engine;
• and
• an evaporated fuel purge amount control section configured so as to control a purge amount which is an amount of said evaporated fuel introduced into said intake passage by said evaporated fuel purge section,
• wherein,
• said evaporated fuel purge section includes a canister, which is disposed in a purge passage communicating between said fuel tank and said intake passage, and which adsorbs said evaporated fuel generated in said fuel tank,
• said target air-fuel ratio setting section is configured:
• so as to obtain an estimated adsorbed amount of said evaporated fuel which is a value indicative of an amount of said evaporated fuel adsorbed in said canister;
• so as to set said target rich air-fuel ratio to a first target rich air-fuel ratio smaller than stoichiometric air-fuel ratio and set said target lean air-fuel ratio to a first target lean air-fuel ratio larger than the stoichiometric air-fuel ratio, when said estimated adsorbed amount of said evaporated fuel is smaller than a predetermined amount;
• and
• so as to set said target rich air-fuel ratio to a second target rich air-fuel ratio smaller than said first target rich air-fuel ratio and set said target lean air-fuel ratio to a second target lean air-fuel ratio larger than said first target lean air-fuel ratio, when said estimated adsorbed amount of said evaporated fuel is equal to or larger than said predetermined amount, and
• said evaporated fuel purge amount control section is configured so as to increase said purge amount as a magnitude of a difference between said target lean air-fuel ratio and said target rich air-fuel ratio becomes larger.